The overall objective of Project 4 is to assess the relationship between exposure to pets, the infant home and gut microbiomes, and allergic asthma at 9 years of age, using an ethnically diverse, population-based general risk birth cohort (the WHEALS cohort). A premise with growing evidence is that lack of exposure to particular patterns of microbial stimuli during early infancy results in a heightened T-helper (Th) 2 response in the maturing immune system, likely due to a suboptimal regulatory capacity, which in turn is associated in childhood with increased immunoglobulin(lg)E, allergy, and clinical allergic conditions such as asthma. Epidemiological studies have revealed that atopic conditions have increased over the latter half of the twentieth century. Humans in earlier centuries had lifestyles associated with closer direct contact with soil, animals and other humans, suggesting exposure to environments with richer and more diverse microbiological burdens. We hypothesize that evolutionary adaptation to such microbial exposures with respect to immune recognition and regulation may result in untoward consequences when humans are presented with the different, and probably more limited, patterns of microbial exposures found in modern Westernized societies. Our theory is that in many settings, pets, as well as farm animals in close proximity, render the home microbiome, or bacterial community composition (BCC,) to be more similar to early 20th century environments with respect to an increased bacterial richness, diversity and a more even distribution of taxa. This home microbiome impacts directly through effects on the infant gastrointestinal tract BCC the immunogenesis of the infant and subsequently the development of clinically important outcomes such as childhood atopic asthma. Using a new technology (the G3 PhyloChipj, capable of cost-effectively identifying, to a great depth, bacteria in environmental and biological samples, our collaborative team has preliminary data suggesting that the presence of dogs and cats is associated with distinct home and infant gut microbiomes characterized by dramatic increases in bacterial diversity, richness and evenness. Using newly measured outcome variables measured by questionnaire and clinical examinations in the WHEALS cohort, in conjunction with PhyloChip analyses of stored infant stool and dust samples, we will test whether distinct patterns of pet exposure, home microbiome and infant gut microbiome are associated with current allergic asthma at age 9 years.